Thermally responsive switch construction and method of making the same



March 22, 1966 H. J. TYLER 3,242,290 THERMALLY RESPONSIVE SWITCHCONSTRUCTION AND METHOD OF MAKING THE SAME Filed Feb. 20, 1962 l IO U IO34| 2 2 20 (I2 32 l 5 6 i 22 3O fi -7 Q l 3 3| 36 28-1 27f 29 25 2| I3I? A; 1 I A 24 i FIG-2 INVENTOR. HUGH JEAN TYLER ATTORNEY United StatesPatent 3,242,290 THERMALLY RESPONSIV E SWITCH CONSTRUC- TION AND METHODOF MAKING THE SAME Hugh Jean Tyler, Jeannette, Pa., assignor toRobertshaw Controls Company, Richmond, Va., a corporation of DelawareFiled Feb. 20, 1962, Ser. No. 174,423 17 Claims. (Cl. 200-417) Thisinvention relates to an improved electrical switch construction and toan improved method for making such a switch construction or the like.

It is well known in the art to provide a fusible electric switch whereinthere is normally an electrical interconnection between the terminals ofthe switch until the switch structure is heated above a predetermined.temperature whereby the electrical current between the terminals isterminated.

For example, such a switch construction can include a movable contactmember normally held in electrical contact with one of the terminalsthereof by a fusible material placed either under tension orcompression. When the fusible material is heated to its melting pointthereof or to a point where it loses its tensile strength the fusiblematerial fails whereby the movable contact arm moves out of contact withits respective terminal to terminate flow of electrical current betweenthe terminals of the switch construction.

However, it has been found that when the fusible material is utilized intension, there is a possibility of premature opening of the switchconstruction due to creepage of the fusible material.

Further, when the fusible material is placed in compression, it has beenfound that similar switch constructions have varying electricalresistance due to variations in the contact pressure of the switchconstructions.

According to the teachings of this invention however, an improvedfusible switch construction is provided wherein the fusible material isactually a conductor in the circuit and thereby eliminates the varyingelectrical resistance of the contacts. Further, there is no prematureopening due to creepage, and expensive gold plating needed to protectcontacts from resistance build-up is eliminated.

Accordingly, it is an object of this invention to provide an improvedswitch construction having one or more of the novel features of thisinvention set forth above or hereinafter shown or described.

Another object of this invention is to provide an improved method formaking such a switch construction or the like.

Other objects, uses and advantages of this invention are apparent from areading of this description which proceeds with reference to theaccompanying drawings forming a part thereof and wherein:

FIGURE 1 is a cross-sectional view of the improved switch constructionof this invention disposed in the normal operating position thereof topermit electrical current to flow between the terminals thereof.

FIGURE 2 is a view similar to FIGURE 1 and illustrates the switchconstruction in the position thereof when electrical current between theterminals is terminated.

FIGURE 3 is a view similar to FIGURE 1 and illustrates one of theassembly steps in forming the switch construction of this invention.

FIGURE 4 is a view similar to FIGURE 3 and illustrates other steps inthe assembly of the switch construction of this invention.

FIGURE 5 is a view similar to FIGURE 4 and illus trates another step inthe method of this invention.

FIGURE 6 is a top plan view of the switch construction illustrated inFIGURE 1.

3,242,290 Patented Mar. 22, 1966 While the various features of thisinvention are hereinafter described as being particularly adaptable toform an electrical switch construction, it is to be understood that thevarious features of this invention can be utilized singly or in anycombination thereof to form other constructions, as desired.

Therefore, this invention is not to be limited to only the embodimentillustrated in the drawings, because the drawings are merely utilized toillustrated one of the wide variety of uses of this invention.

Referring now to FIGURE 1, the improved switch construction of thisinvention is generally indicated by the reference numeral 10 andcomprises an insulating casing or base member 11 carrying a pair ofL-shaped terminals 12 and 13.

The L-shaped terminals 12 and 13 are respectively secured in suitableapertures 14 and 15 formed in the casing 11 and respectively havethreaded bores 16 and 17 formed through the legs 18 and 19 thereof, theother legs 20 and 21 of the terminals 12 and 13 projecting beyond thecasing 11 and having suitable slots 22 and 23 formed therein to formelectrical lead connection means in a manner well known in the art.

A first contact means 24 is carried by the switch construction 10 andcomprises a bolt having a threaded shank portion 25 and an enlarged head26, the shank portion 24 being threadedly received in the bore 17 of theterminal 13 and sandwiching a pair of contact legs or arms 27 and 28 anda spacer 29 between the enlarged head 26 thereof and the leg 19 of theterminal 13.

The contact arm 27 is rigid and forms a support while the contact arm 28is flexible and normally tends to be disposed fiat against the contactarm or support 27 for a purpose hereinafter described.

A second contact means 30 is carried by the switch construction 10 andcomprises a threaded member threadedly received in the threaded bore 16in the leg 18 of the terminal 12, the contact means 30 having abifurcated end 31 to provide means for initially adjusting the positionof the other end 32 of the contact means 30 relative to the contact armor support 27 for a purpose hereinafter described.

The flexible contact arm 28 is normally held in the position illustratedin FIGURE 1 by solder means 33 and 34, the solder means 33 being securedto one side of the contact arm 28 and to the end 32 of the contact means30 whereby the solder means 33 is placed under tension by the naturalresiliency of the contact arm 28 tending to move away from the contactmeans 30 toward the support 27. The solder means 34 is secured to theother side of the contact arm 28 and to the support 27 whereby thesolder means 34 is placed under compression by the natural resiliency ofthe contact arm 28 tending to move toward the support 27.

The solder means 34 has a melting point lower than the melting point ofthe solder means 33 while the solder means 33 has its tensile propertiesreduced when heated to a temperature corresponding to the meltingtemperature of the solder means 34.

While the switch construction 10 can be utilized in any desiredapplication to provide means for terminating flow of electrical currentthrough a circuit when the temperature of the switch construction 10reaches the meltng point of the solder means 34, one such use for theswitch construction 10 would be in conventional, domestic, gas-firedclothes dryers or the like.

For example, in such a gas-fired clothes dryer or the like, a normallyburning pilot thereof energizes a thermocouple lead leading to anelectrical coil of a safety valve whereby the safety valve remains openas long as the thermocouple is being heated so that .gas can flow to themain burner of the clothes dryer. By placing the switch construction ofthis invention in the thermocouple lead, the same will terminate thecurrent flowing to the safety valve should the temperature of the dryerexceed safe limits thereof due to exhaust blockage, broken fan belt orother reasons whereby the safety valve would close and prevent gas frombeing fed to the main burner of the clothes dryer.

Since the switch construction 10 of this invention is non-recycling,corrective servicing of the clothes dryer is necessary before it isagain put into operation whereby it is impossible to operate the dryeruntil the cause for the high temperatures has been remedied.

The operation of the switch construction 10 will now be described.

When the switch construction 10 is disposed in the position illustratedin FIGURE 1, electrical current is adapted to flow between the terminals12 and 13 because the contact arm 28, being electrically interconnectedto the contact means 24, is placed in electrical connection with thecontact means 30 by the solder means 33, the solder means 33 comprisingan electrical conductor whereby varying electrical resistance betweenthe contact arm 28 and the contact means 30 is eliminated because thesolder means 33 is secured respectively to the contact arm 28 and to thecontact means 30.

Further, the solder means 34 is an electrical conductor wherebycurrentcan flow from the contact means 30 to the support 27 which iselectrically interconnected to the contact means 24.

In this manner, expensive gold plating needed to protect electricalcontacts from resistance build-up is elimihated by this inventionbecause the solder means 33 and 34 provide good electrical connectionbetween the termirials 12 and 13 of the switchconstruction 10.

Further, even though the solder means 33 is placed under tension, nopremature opening of the switch construction 10 from creepage ispossible because the solder means 34 is placed under compression to holdthe contact arm 28 in place.

As long as the contact arm 28 of the switch construction 10 remains inthe position illustrated in FIGURE 1, electrical current is adapted toflow between the terminals 12 and 13 thereof.

However, should the temperature of the atmosphere surrounding the switchconstruction 10 heat up to such a temperature to cause the solder means34 to fuse or melt, the solder means 34 collapses and the solder means33, although remaining solid, loses at least some of its tensileproperties whereby the natural resiliency of the contact arm 28 movesthe contact arm 28 toward the support 27 in the manner illustrated inFIGURE 2 and makes a smooth break across the solder means 33 to move outof electrical connection with the contact means 30 to terminate the flowof electrical current between the terminals 12 and 13.

Because the solder means 33 is not fused or melted at the temperaturecausing fusing or melting of the solder means 34, a clean break iseffected across the solder means 33 by the moving contact arm 28 wherebyno stringers of the solder means 33 are provided which would stillpermit electrical connection between the contact means 28 and thecontact means 30 when the contact arm 28 is moved to the positionillustrated in FIGURE 2.

Therefore, it can be seen that an improved electrical switchconstruction of this invention is provided which will accuratelyterminate flow of electrical current between the terminals thereof whenthe temperature of the switch construction reaches the melting point ofthe fusible material 34 because the melting point of the solder means 34can be predetermined.

Further, because the switch construction 10 opens when the fusiblematerial 34 fuses or melts, a more accurate operation thereof iseffected than when a switch construction opens solely on a fusiblematerial losing its tensile properties at a particular temperaturebecause the resilient properties for movable contact arms can vary.

The method of this invention for making the switch construction 10 ofFIGURE 1 will now be described and reference is made to FIGURES 3-5.

Preferably, but not necessarily, the solder means 33 is first placed onthe end 32 of the contact means 30 before the contact means 30 isassembled to the switch construction 10 in the manner illustrated inFIGURE 3.

When the contact means 30 is disposed in the position illustrated inFIGURE 3, a suitable shim 35 is forced between the support 27 and thecontact arm 28 to hold the contact arm 28 in its biased conditionagainst the solder means 33 carried by the contact means 30 in themanner illustrated in FIGURE 4, the shim 35' being formed of anysuitable material, such as Teflon or the like.

After the shim 35 has been placed in the position illustrated in FIGURE4 to hold the contact arm 28 in contact with the solder means 33, thecontact means 30 is adjusted toward the contact arm 28 by rotating thesame through a quarter turn or the like to press the solder means 33against the contact arm 28 with a certain pressure.

Thereafter, solder paste 36 is disposed around the contact means 30 andthe terminal 12 as Well as around the shank and head 26 of the contactmeaiis 34 in the manner illustrated in FIGURE 4.

Subsequently, a wire or the like of the solder means 34 is insertedbetween the support 27 and the contact arm 28 in the manner illustratedin FIGURE 5.

Thereafter, the entire switch construction illustrated in FIGURE 5 isheated to melt all of the solder means 33, 34, and 36. For example, theswitch construction as illustrated in FIGURE 5 can be placed upright inthe position shown in an oven or the like and heated to 507 to 525 F.for approximately three to five minutes.

In this manner, the solder means 33, 34, and 36 fully wet the desiredsurfaces of the switch construction 10 so that upon subsequent removalof the switch construction 10 from the oven to cool and solidify thesolder means 33, 34, and 36, the solder means 33 is fully secured to thecontact arm 28 and to the contact means 30 while the solder means 34 isfully secured to the contact arm 28 and to the support 27 to hold thecontact arm 28 in the position illustrated in FIGURE 1 when the shim 35is subsequently removed. In addition, the solder means 36 firmly holdsthe contact means 30 and 24 in place in the proper adjusted positionsthereof.

Prior to the cooling of the heated switch construction 10, the switchconstruction 10 can be immersed in hot water to remove all solder fluxtherefrom, as desired.

Therefore, it can be seen that the switch construction 10 of thisinvention can be made in a relatively simple and a relatively rapidmanner to produce the switch construction 10 which is not onlyeconomical but which is also accurate in the operation thereof.

Accordingly, it can be seen that an improved electrical switchconstruction is provided by this invention as well as an improved methodof making such a switch construction or the like.

While the form of the invention now preferred has been disclosed asrequired by the statutes, other forms may be used, all coming within thescope of the claims which follow.

What is claimed is:

1. A switch construction comprising a casing, a pair of electricalcontact means carried by said casing, a support carried by said casing,a resilient contact arm carried by one of said contact means andnormally disposed out of contact with the other contact means, a firstmeans disposed between said contact arm and said other contact means andholding said contact arm in a biased condition toward said other contactmeans whereby said contact arm is placed in electrical connection withsaid other contact means and said first means is placed under ten sion,and a second means disposed between said support and said contact armand holding said contact arm in said biased condition toward said othercontact means whereby said second means is placed under compression,said second means having a lower melting point than said first means andsaid first means having its tensile properties reduced when heated tothe melting point of said second means whereby electrical connectionbetween said contact means is terminated when said switch constructionis heated to said melting point of said second means to cause saidcontact arm to break said first means and move away from said othercontact means.

2. A switch construction comprising a casing, a pair of electricalcontact means carried by said casing, a support arm carried by one ofsaid contact means, a resilient contact arm carried by said one contactmeans and normally disposed out of contact with the other contact means,a first means disposed between said contact arm and said other contactmeans and holding said contact arm in a biased condition toward saidother contact means whereby said contact arm is placed in electricalconnection with said other contact means and said first means is placedunder tension, and a second means disposed between said support arm andsaid contact arm and holding said contact arm in said biased conditiontoward said other contact means whereby said second means is placedunder compression, said second means having a lower melting point thansaid first means and said first means having its tensile propertiesreduced when heated to the melting point of said second means wherebyelectrical connection between said contact means is terminated when saidswitch construction is heated to said melting point of said second meansto cause said contact arm to break said first means and move away fromsaid other contact means.

3. A switch construction as set forth in claim 2 wherein said firstmeans electrically interconnects said contact arm with said othercontact means.

4. A switch construction as set forth in claim 2 wherein electricalterminals are respectively electrically interconnected to said contactmeans.

5. A switch construction as set forth in claim 2 wherein said othercontact means is adjustably carried by said casing.

6. In combination, a casing, a pair of contact means carried by saidcasing, a movable spring contact arm electrically interconnected to oneof said contact means and normally tending to be disposed in a positionaway from the other of said contact means, a first means disposed on oneside of said contact arm and tending to hold said contact arm in anotherposition thereof toward said other contact means whereby said contactarm is electrically interconnected to said other contact means and saidfirst means is placed under tension, and a second means disposed on theother side of said contact arm and tending to hold said contact arm insaid other position thereof whereby said second means is placed undercompression, said second means having a lower melting point than saidfirst means whereby electrical connection between said contact means isterminated when said first and second means are heated to said meltingpoint of said second means to cause said contact arm to overcome theholding force of said first means and move away from said other contactmeans.

7. A combination as set forth in claim 6 wherein said first means is anelectrical conductor.

8. A combination as set forth in claim 6 wherein said second means is asolder.

9. A combination as set forth in claim 6 wherein said first and secondmeans are solder.

10. In a switch construction, a movable spring contact arm disposed inone position thereof and tending to move to another position thereof, afirst means secured to one side of said contact arm and to said switchconstruction whereby said first means is placed under tension, and asecond means secured to the other side of said contact. arm and to saidswitch construction whereby said second means is placed undercompression, said second means having a lower melting point than saidfirst means whereby said contact arm moves to said other positionthereof by breaking said first means when said first and second meansare heated to said melting point of said second means.

11. In a switch construction as set forth in claim 10, said first meanshaving its tensile properties reduced when heated to the meltingtemperature of said second means.

12. A method for making a switch construction comprising the steps ofplacing a first means on one contact means of a switch structure,holding a movable contact arm in contact with said first means, saidcontact arm being electrically interconnected to another contact meansof said switch structure and normally tending to move away from said onecontact means, placing a second means between said contact arm and asupport of said switch structure, said second means having a lowermelting point than said first means, and securing said means to saidcontact arm whereby said contact arm is held in one position thereof bysaid first and second means to electrically interconnect said contactmeans together until said second means is heated to said melting pointthereof to terminate said electrical interconnection between saidcontact means.

13. A method for making a switch construction comprising the steps ofplacing a first solder means on one contact means of a switch structure,holding a movable contact arm of said switch structure in contact withsaid first solder means, said contact arm being electricallyinterconnected to another contact means of said switch structure andnormally tending to move away from said one contact means, placing asecond solder means between said contact arm and a support of saidswitch struc- .ture, said second solder means having a lower meltingpoint than said first means, securing said solder means to said contactarm and respectively to said one contact means and said support wherebysaid contact arm is held in one position thereof by said first andsecond means to electrically interconnect said contact means togetheruntil said second means is heated to said second melting point thereofto terminate said electrical interconnection between said contact means.

14. A method for making a switch construction comprising the steps ofplacing a first solder means on one contact means of a switch structure,holding a movable contact arm of said switch structure in one positionthereof and in contact with said first solder means, said contact armbeing electrically interconnected to another contact means of saidswitch structure and normally tending to move away from said one contactmeans, placing a second solder means betwen said contact arm and asupport of said switch structure, said second solder means having alower melting point than said first solder means, heating said switchstructure to a temperature of at least the melting point of said firstsolder means while still holding said contact arm in said one positionthereof whereby said solder means wets said contact arm and respectivelywets said one contact means and said support, cooling said switchstructure to solidify said solder means so that said solder means tendsto hold said contact arm in said one position thereof, and ceasing tohold said contact arm in said one position thereof whereby said soldermeans holds said contact arm in said one position thereof until saidswitch structure is heated to the melting point of said second soldermeans.

15. A method as set forth in claim 14 wherein said step of holding saidcontact arm in said one position thereof includes the step of insertinga member between said support and said contact arm.

16. A method as set forth in claim 14 wherein said first solder meanshas its tensile properties reduced when heated to the meltingtemperature of said second solder means.

17. A method as set forth in claim 14 wherein said one contact means isadjusted relative to a casing of said switch structure to a desiredposition thereof and is subsequently secured in said desired position.

Metzgar 200-123 Bussmann 200123 McAlister 200142 Milton et a1. 200-123Milton et a1. 200-442 BERNARD A. GILHEANY, Primary Examiner.

1. A SWITCH CONTRACTION COMPRISING A CASING, A PAIR OF ELECTRICALCONTACT MEANS CARRIED BY SAID CASING, A SUPPORT CARRIED BY SAID CASING,A RESILIENT CONTACT ARM CARRIED BY ONE OF SAID CONTACT MEANS ANDNORMALLY DISPOSED OUT OF CONTACT WITH THE OTHER CONTACT MEANS, A FIRSTMEANS DISPOSED BETWEEN SAID CONTACT ARM AND SAID OTHER CONTACT MEANS ANDHOLDING SAID CONTACT ARM IN A BIASED CONDITION TOWARD SAID OTHER CONTACTMEANS WHEREBY SAID CONTACT ARM IS PLACED IN ELECTRICAL CONNECTION WITHSAID OTHER CONTACT MEANS AND SAID FIRST MEANS IS PLACED UNDER TENSION,AND A SECOND MEANS DISPOSED BETWEEN SAID SUPPORT AND SAID CONTACT ARMAND HOLDING SAID CONTACT ARM IN SAID BIASED CONDITION TOWARD SAID OTHERCONTACT MEANS WHEREBY SAID SECOND MEANS IS PLACED UNDER COMPRESSION,SAID SECOND MEANS HAVING A LOWER MELTING POINT THAN SAID FIRST MEANS ANDSAID FIRST MEANS HAVING ITS TENSILE PROPERTIES REDUCED WHEN HEATED TOTHE MELTING POINT OF SAID SECOND MEANS WHEREBY ELECTRICAL CONNECTIONBETWEEN SAID CONTACT MEANS IS TERMINATED WHEN SAID SWITCH CONSTRUCTIONIS HEATED TO SAID MELTING POINT OF SAID SECOND MEANS TO CAUSE SAIDCONTACT ARM TO BREAK SAID FIRST MEANS AND MOVE AWAY FROM SAID OTHERCONTACT MEANS.